1. Preheat oven to 160° C.2. Coarsely grind the hazelnuts.3. Cream together ½ cup butter and brown sugar in a bowl using an electric beater till light and fluffy.4. Break eggs in another bowl. Add vanilla essence and whisk well. 5. Sift together ½ cup + 1 tablespoon flour, powdered sugar, 2-3 tablespoons semolina, baking powder and salt in another bowl.6. Add the egg mixture gradually to the butter-sugar mixture and whisk well, scraping the sides of the bowl.7. Add ground hazelnut to the batter and mix. Add the flour mixture and fold well. Add olive oil and mix well. 8. Grease a round spring bottom mould with some butter and dust with some semolina. Pour the batter and tap. Put the tin in the preheated oven and bake for 30-35 minutes. Remove from oven, cool and demould.9. Dust with some icing sugar, cut into wedges and serve.